1. Field of the Invention
The invention relates to crossed-field microwave electron interaction devices.
2. Description of the Prior Art
Crossed-field electron interaction devices of the traveling wave type commonly include a periodic slow wave electromagnetic energy propagating structure such as a delay line. Mutually perpendicular unidirectional electric and magnetic fields in the interaction region combine to provide for interaction of electrons, emitted from a coaxial cathode, in an energy exchanging relationship with electromagnetic waves propagating along the slow wave structure. The principle of interaction between the electrons launched from the cathode and the electromagnetic waves is based on the synchronization of the electron beam velocity with the phase velocity of the waves on the slow wave structure to result in amplification and/or oscillation of high frequency electromagnetic energy. A DC potential is applied between the cathode and slow wave structure and the magnetic field is applied parallel to the axis of the cathode or transverse to the electrical field. Substantially high power microwave energy has been generated by such devices referred to as "Amplitrons."
The crossed-field devices are utilized as forward or backward wave amplifiers or oscillators in electromagnetic energy systems. The fields of the wave energy propagating along the slow wave structure provides space harmonic waves which travel with different phase velocities. By varying the electron velocity, synchronization with a desired phase velocity of the space harmonic wave component may be achieved. The phase and group velocities of some of the space harmonics are oppositely directed and these harmonics are referred to as backward waves. The other space harmonics are referred to as forward waves and are characterized in that the phase and group velocities are in the same direction. Amplification and generation of energy is obtained by the interaction between the electrons and the forward or backward wave. The group of devices referred to as M-type amplifiers are characterized in that the electron beam in the interaction region interact with space harmonic waves of either the forward or backward wave type. In such devices cold cathodes have not been successfully employed of such materials as tungstenthoria cermet, oxide-coatings, nickel, platinum coating and copper. Such cold cathodes have a high secondary electron emission ratio. The use of cold cathodes results in the elimination of electrical supplies required for the heater in the conventional thermionic-heated type cathodes.
The cold cathode is activated by an RF signal drive and sufficient numbers of gas molecules in the tube interaction region are typically present in the highly evacuated crossed-field devices to initiate bombardment of the cathode and provide for the emission of the secondary electrons. The electrons are circulated through the interaction region as a spoke-like space charge to interact with the waves on the slow wave structure. Efficiencies in the order of 70-75 percent are attainable with the Amplitron type devices and many thousands of watts and megawatts of power are attainable. Further particulars regarding the prior art crossed-field devices may be had by referring to U.S. Pat. Nos. 3,096,457 issued July 2, 1963 to W. A. Smith, Jr. and G. H. MacMaster and 3,646,388, issued Feb. 29, 1972 to K. W. Dudley and G. H. MacMaster, all assigned to the assignee of the present invention.
To develop high powers with low voltage operating requirements and high efficiencies is a continuing need in the microwave energy field. In light of the developing energy crisis throughout the world considerable effort is being undertaken in the evaluation of space oriented power stations utilizing solar energy. Such energy is converted into electrical energy which is in turn converted into microwave energy by sources provided on a space station and the microwave energy is beamed through space to earth stations to be converted into electrical power for distribution. An example of the space application is found in U.S. Pat. No. 3,781,647 issued Dec. 25, 1973 to Peter E. Glaser. The efficient conversion of electrical energy into microwave energy for transmission to earth stations warrents the use of high power crossed-field devices. Since radiation cooling, instead of liquid cooling normally used for high power tubes, is desired in space applications, an upper limit on the capability of present day crossed field devices exists. For the space applications it is desirable to provide crossed-field devices operating at power levels in the megawatt level. The primary objective of the present invention, therefore, is the provision of a crossed-field device having high power capabilities for possible utilization in solar energy-electrical power conversion systems or other similar energy-related programs.